1. Field of the Invention
The present invention relates generally to intervertebral disc reconstruction or repair methods. More specifically, the present disclosure relates to a method for increasing the stiffness of an intervertebral disc between adjacent vertebral bodies of a spine.
2. Background of the Invention
In human anatomy, the spine is a generally flexible column that can take tensile and compressive loads. The spine also allows bending motion and provides a place of attachment for keels, muscles and ligaments. Generally, the spine is divided into three sections: the cervical spine, the thoracic spine and the lumbar spine. The sections of the spine are made up of individual bones called vertebrae. Also, the vertebrae are separated by intervertebral discs, which are situated between adjacent vertebrae.
The intervertebral discs function as shock absorbers and as joints. Further, the intervertebral discs can absorb the compressive and tensile loads to which the spinal column may be subjected. At the same time, the intervertebral discs can allow adjacent vertebral bodies to move relative to each other a limited amount, particularly during bending, or flexure, of the spine. Thus, the intervertebral discs are under constant muscular and/or gravitational pressure and generally, the intervertebral discs are the first parts of the lumbar spine to show signs of deterioration.
The intervertebral disc functions to stabilize the spine and to distribute forces between vertebral bodies. The intervertebral disc is composed of three structures: the nucleus pulposus, the annulus fibrosis, and two vertebral end plates. These components work to absorb the shock, stress, and motion imparted to the human vertebrae. The nucleus pulposus is an amorphous hydrogel with the capacity to bind water. The nucleus pulposus is maintained within the center of an intervertebral disc by the annulus fibrosis, which is composed of highly structured collagen fibers. The vertebral end plates, composed of hyalin cartilage, separate the disc from adjacent vertebral bodies and act as a transition zone between the hard vertebral bodies and the soft disc.
Intervertebral discs may be displaced or damaged due to trauma or disease. Disruption of the annulus fibrosis may allow the nucleus pulposus to protrude into the vertebral canal, a condition commonly referred to as a herniated or ruptured disc. The extruded nucleus pulposus may press on a spinal nerve, which may result in nerve damage, pain, numbness, muscle weakness, and paralysis. Intervertebral discs may also deteriorate due to the normal aging process. As a disc dehydrates and hardens, the disc space height will be reduced, leading to instability of the spine, decreased mobility and pain.
One way to relieve the symptoms of these conditions is by surgical removal of a portion or the entire intervertebral disc. The removal of the damaged or unhealthy disc may allow the disc space to collapse, which would lead to instability of the spine, abnormal joint mechanics, nerve damage, as well as severe pain. Therefore, after removal of the disc, adjacent vertebrae are typically fused to preserve the disc space. Spinal fusion involves inflexibly connecting adjacent vertebrae through the use of bone grafts or metals rods. Because the fused adjacent vertebrae are prevented from moving relative to one another, the vertebrae no longer rub against each other in the area of the damaged intervertebral disc and the likelihood of continued irritation is reduced. Spinal fusion, however, is disadvantageous because it restricts the patient's mobility by reducing the spine's flexibility, and it is a relatively invasive procedure.
Attempts to overcome these problems have led researchers to investigate the efficacy of implanting an artificial intervertebral disc to replace, completely or partially, the patient's damaged intervertebral disc. Disc replacement surgery generally involves removing the disc or damaged portion thereof and placement of an artificial disc in the evacuated disc space. Some desirable attributes of a hypothetical implantable disc include axial compressibility for shock absorbance, excellent durability to avoid future replacement, minimally invasive placement of the artificial disc to reduce post-operative discomfort, and biocompatibility. Existing artificial intervertebral discs include, for example, mechanically based (e.g. comprising rotational surfaces or springs), polymer based, and biopolymer based artificial discs.
Among the polymer based artificial intervertebral discs are several devices that utilize a flowable polymer. One example of such a device is U.S. Pat. No. 3,875,595, incorporated herein by reference in its entirety, which discloses an intervertebral disc prosthesis comprising a flexible bladder-like member that is inserted into the evacuated disc space. The prosthesis is anchored to the two adjacent vertebrae through the use of studs inserted into the bone and filled with a fluid, plastic, or hydrogel until the bladder expands to fill the evacuated disc space.
In another example, U.S. Pat. No. 6,264,659, incorporated herein by reference in its entirety, the nucleus pulposus is removed. A thermoplastic material is heated until its viscosity is sufficiently reduced to allow it to be injected under pressure into the annulus fibrosis. The thermoplastic then cools to body temperature and stiffens but retains sufficient resiliency to provide cushioning of the vertebrae and joint movement.
U.S. Pat. No. 6,187,048, incorporated herein by reference in its entirety, discloses an intervertebral disc implant wherein the nucleus pulposus is removed and a flowable polymer is injected into the evacuated annulus fibrosis. The flowable polymer is caused to cure in situ, forming a shaped, resiliently deformable prosthesis.
U.S. Pat. No. 6,140,452, incorporated herein by reference in its entirety, discloses an intervertebral disc implant wherein a multi-part polyurethane biocompatible polymer is injected into the evacuated disc space, preferably through the use of a cannula and arthroscope. The flowable composition then is cured in place.
Related art load bearing intervertebral disc implants, both prefabricated type implants and injectable implants formed in situ, are inserted into patients after a complete or partial removal of disc material. When disc material is removed, a healthy part of the disc is often taken, eradicating the function of the joint.
Preformed disc implants may tear or otherwise be damaged during implantation. Further, once implanted, many disc implants such as those formed of hydrogel may be expelled from the disc space through an annular defect, or other annular opening.
In-situ cured polymers inserted into the disc under pressure can leak the material into sensitive adjacent areas. Others have attempted to remedy the leakage potential after accessing the nucleus pulposus through the annulus and removing a portion of the nucleus pulposus by creating a seal to prevent the material from leaking through the created opening, an example of which is US 2006/0004458, incorporated herein by reference in its entirety.
Treatment to the disc in a most non-invasive procedure is preferred. This method allows the maximum amount of healthy tissue to remain intact, and for maximum retention of the normal neurological function.
A need exists for a method that increases the stiffness of an intervertebral disc that has sufficient continuity so as to retain a flowable material subsequently injected into the disc, and retains the material while it becomes a load bearing implant, and which preferably does so without removing disc material, and which preferably allows the disc to retain normal joint function and motion.
The description herein of problems and disadvantages of known apparatus, methods, and devices is not intended to limit the invention to the exclusion of these known entities. Indeed, embodiments of the invention may include one or more of the known apparatus, methods, and devices without suffering from the disadvantages and problems noted herein.